Patent GB-1161903-A (GB)
Title: Method and Apparatus for Bonding the Surfaces of Thermoplastic Resin.
Inventor: BEIK HERMAN
IPC: B29C65/50
Filed: 1966-07-12
Abstract: 1,161,903. Seaming non-metallic sheet material. W. BAHLSEN. 12 July, 1966, No. 7396/69. Divided out of 1,161,901. Heading B5K. [Also in Division B8] In a method of heat bonding together two sheet materials, at least one of which is of synthetic resinous material and has a thermoplastic surface, the heat required for bonding the surface(s) is produced by eddy currents induced in a metal strip or foil which lies between the surfaces to be bonded and the materials to be bonded are pressed together by a pressure tool whilst the thermoplastic surface(s) is/are plastic. A metal foil free of any coating may be introduced between the surfaces to be bonded which may consist of or be coated with a thermoplastic resin. Thermoplastic coatings may be provided additionally or alternatively on both sides of the metal foil. Alternatively, one of the surfaces to be bonded may be provided with a facing of metal foil having a thermoplastic coating on its exposed side. The materials to be bonded may be resin-coated cardboard or paper. In one embodiment, Fig. 1, a rectangular blank 1 of thermoplastic material or cardboard provided with a thermoplastic coating is bent into cylinder shape with a metal strip 2 inserted between the overlapping edges thereof. The blank 1 is moved over a coil 3 embedded in an insulator 4 and which may be hairpin shaped and comprise a cooled pipe. Pressure is applied by a tool 5 which connects the coil 3 to a highfrequency generator 6 as soon as it contacts the overlapped cylinder edges so that a brief current pulse is applied to the coil 3. The foil strip may be supplied continuously from a roll, Fig. 8 (not shown). In a modification, Fig. 4, the overlapping cylinder edges are introduced between the leg portions of a hairpin coil 7, the upper leg being loosely supported in a reciprocable tool, Fig. 5 (not shown). In a further modification, Figs. 6 and 7 (both not shown), hairpin coils (12), (13) are disposed above and below the overlapping edges during bonding. The method is applicable to closing filled plastics bags and the metal strip or foil can be subsequently used as a tear strip. In a further embodiment, Fig. 9, to form a welded closure seam along edge portions of a filled container completely lined with aluminium foil, the container is moved continuously through a high-frequency magnetic field produced by hairpin coils embedded in members 22, 23. Pressure is applied by rollers simultaneously with or subsequent to the action of the heat. In another embodiment, Fig. 11, to close a cylindrical container 27, a metal foil 26 is provided on the upper edge of the container body and is bonded to the edge 28 of a lid using a circular induction coil 29. Helical or spiral induction coils may also be used to seal package closures, Figs. 12 and 13 (both not shown). In a still further embodiment, Fig. 14, a cylindrical tube is produced continuously by forming a paper or cardboard web 33 drawn off from a roll into a cylindrical shape about a mandrel 34 with a foil strip 35 between the overlapped edges. A stationary induction coil 39 is disposed above the welding zone, e.g. between pressure rollers 37, 38, to form the longitudinal seam. Subsequently, a rotating cutter 40 cuts the tube to length. In a modification, the foil strip comprises iron foil and heating thereof is effected by passage through the gap 42 of an electromagnet 43, Fig. 15, having a coil 44 and disposed between the foil supply roll 36 and a guide roller 41, Fig. 14. Alternatively, the foil strip is passed through an induction coil, Fig. 16 (not shown). In yet another embodiment, Fig. 21, a container body is bent about a mandrel to tubular form with the overlapping edges disposed between the central legs 111, 1111 of an electromagnet 112 and a co-operating iron part 112<SP>1</SP> mounted in the mandrel in a plaster resin 115. The magnet 112 is mounted on a lever (114), Fig. 20 (not shown), by which it is moved towards and away from the mandrel. A bottom or lid 103, Fig. 22, is welded to the container body 101, which has a metal foil strip 107 provided at each end thereof, by passage of the assembled lid and body through the gap 116 of a magnet 117 by rotation of the body 101. Rollers (118), (119), Fig. 23 (not shown), subsequently apply pressure to effect the bond. In a modification, Fig. 24, the magnet 121 is cup-shaped. In an automatic machine for making tubular container bodies, Fig. 26, a web 201 of paper or cardboard having a thermoplastic coating is drawn from a roll 204 by supply rolls 203 controlled by a photo-electric device 204. An aluminium foil 206 from a roll 205 is bonded to one edge of the web 201 by a device 207 which applies a short heating pulse. A blank is punched from the web by a knife 208 and is grasped by tongs 209 and advanced thereby to abut a stop 210. A ram 211, Fig. 28, presses the blank against a stationary mandrel 212 and is wrapped therearound by jaws 212, 213 having portions 216, 217 shaped to match the mandrel surface. The jaws 212, 213 move in guides 214, 215 and have their upper ends rounded or provided with rollers 218, 219. A sealing jaw 220 comprising an induction coil is lowered and eddy currents are induced in the metal foil located between the overlapping blank edges. In modifications, the jaw 220 is a heated jaw or is an electrode for high-frequency welding, a complementary electrode being provided in the mandrel 212. After welding, the blank is stripped from the mandrel 212 by jaws (221), (222), Fig. 30 (not shown), having projections (223), (224) to slide in grooves 225, 226, Fig. 28, in the mandrel 212 and is telescoped over a mandrel 227 of a machine 228 which is then indexed to carry the container body to the next station. In a mchine for forming a flat web 503 into a tube which, in the course of its formation, is filled and then closed, Fig. 33, apolyvinylchloride web 503, provided with spaced transverse metal foil strips (504), Figs. 31 and 32 (both not shown), and a continuous longitudinal metal foil strip (505), is drawn from a roll 502 to pass over stationary rollers 509, 510, 511 and a movable roller 512 to a shaping shoulder 513 and a tube 517 is formed in a gap 514 between jaws 515 of the shoulder 513 and a guide tube 516 with the strips (504), (505) lying internally of the tube 517. The longitudinal seam is produced by a device 518 and the transverse seams are produced by devices 523, 523<SP>1</SP> disposed on links 521, 521<SP>1</SP> of endless chains 522, 522<SP>1</SP>. Measured quantities of materials to be packaged are fed into a hopper 516<SP>1</SP> and through the tube 516. Completed packages are severed from the tube 517 at position III. The device 518, Figs. 33 and 37, comprises ferrite cores 535, 536 electrically excited by a coil 537 to heat the foil 505 by induction of eddy currents therein. Rollers 519, 520 are pressed against the seam 508, by springs 541, 542. The devices 523, 523<SP>1</SP>, Figs. 33 and 41, also comprise ferrite cores 545, 546 excited by a coil 547 and springs 551, 552, Fig. 42, urge the device 523 towards the device 523<SP>1</SP> and bear against a member 553 guided in slots 554, 555 provided in the link 521. Rollers 556, 557 are carried by the member 553 and, during sealing, rest against rails 558, 559. Rollers 562, 563 on the links 521, 5211 run in guides 560, 561 to guide the chains 522, 522<SP>1</SP>. A knife 564 is provided in a recess 565 in the link 521<SP>1</SP> and the core 546 and is actuated by a magnet 566 through levers 567 and rollers 568 to sever the individual filled packages. Springs 569 retract the knife 564 after each cutting operation. In a modification, instead of previously applying the longitudinal foil strip to the web 503, a strip 528, Fig. 33, is fed from a roll 529 into the gap at the overlap during formation of the tube. Alternatively, if the web 503 is provided with a full-surface backing of metal foil then the strips can be entirely omitted.